The use of solvents having a high aromatic content (such as white spirits) has been known for some considerable time in a great number of applications where good solvency characteristics are required (see “Directory of solvents”, Edited by B. P. Whim and P. G. Johnson, Blackie Academic and Professional).
However, solvents having a high aromatic content, although affording good solvency, are disadvantageous from a health and environmental viewpoint. For instance, volatile organic components (VOCs) containing aromatics that are emitted when using solvents such as white spirit are responsible for the increased creation of ozone in the troposphere, when compared for example to saturated products (see “Photochemical ozone creation potentials for a large number of reactive hydrocarbons under European conditions”, R. G. Derwent, M. E. Jenkin and S. M. Saunders, Atmospheric Environment, Vol. 30, No. 2, 181–199, 1996). In addition, aromatic-containing compounds and ozone are poisonous. Thus, high-aromatic solvents are hazardous to the health of the user and can be damaging to the environment. According to the European Chemical Industrial Council (CEFIC) scheme for environmental classification of solvents, some white spirit grades are classified as dangerous for the environment. The POCPs (Photochemical Ozone Creation Potentials) of the aromatic compounds in white spirit are higher than the POCPs of aliphatic hydrocarbons and esters (see “Photochemical ozone creation potentials for a large number of reactive hydrocarbons under European conditions”, R. G. Derwent, M. E. Jenkin and S. M. Saunders, Atmospheric Environment, Vol. 30, No. 2, 181–199, 1996). However, solvents having a lower content of aromatics are considered to be less detrimental to health and environment.
It is thus desirable to use solvents that do not contain aromatic compounds, or have a low aromatic content. Such solvents have been proposed in the past (see “Directory of solvents”, Edited by B. P. Whim and P. G. Johnson, Blackie Academic and Professional). Hydrocarbons having an aromatic content of less than 1% vol. are not classified as dangerous under the CEFIC classification and they show POCP values lower than aromatics, as indicated above. FR 2511019A discloses a diluent comprising a mixture of white spirit with less than 5% aromatics and another solvent. EP 0495348A describes a composition for removing the protective coating from new cars, containing isoparrafin having not more than 0.5 wt % of aromatics. However, although the volatility of such solvents is similar to that of white spirits, there is a problem with such solvents, since they have a low solvency power. The use of such solvents is thus limited.
It is known that the solvency power of ester compounds is high (see C. Nielsen, “Vegetable esters—cleaning agents in the paint and ink industry”, presentation by C. Nielsen, Institute Maurice, Brussels-Anderlecht, Belgium 1999; and “Metal cleaning and degreasing with vegetable-based fatty acid esters”, Demi Theodori/Chemiewinkel, University of Amsterdam). WO 91/06690 describes a mixture for cleaning printed circuit boards containing aliphatic hydrocarbons and organic compounds with polar groups, such as esters. JP 05 098297 discloses a detergent comprising 20–90% hydrocarbon, 5–50% ester and 5–40% surfactant. In addition, esters generally do not contain harmful aromatics and VOCs and therefore are not classified as compounds dangerous to the environment or health. However, whilst the solvency power of esters is high, they have low volatility. This characteristic limits their use as solvents, because they have very long evaporation times making them impractical for many purposes. For example, when esters are used as solvents for some paint applications, the paint will take far too long to dry and may in fact remain sticky.